Flexible/printable electronics have received a great attention in the past decade mainly at low frequency below MHz ranges for consumer electronics such as displays, portable devices and RFIDs [see for example R. Reuss, et al “Large-Area, Flexible Macroelectronics,” Proc. IEEE, vol. 93, no. 7, pp. 1239-1256, 2005; Misra, V., “Emerging technologies in flexible electronics,” Electron Devices Meeting, pp. 437-437, 2005; or Kim, D., Moon, J., “Highly Conductive Ink Jet Printed Films for Nanosilver Particles for Printable Electronics” Electrochemical and Solid-State Letters, Vol. 8, pp. 30-34, September 2008].
The main drives for the technology include low-cost manufacturing through roll-to-roll process, lightweight, mechanical reliability, and bendable for irregular surfaces. Flexible/printable electronic technology is a key enabler for many demanding electronic systems which have constraint requirement such as space, weight and power (SWaP) in addition to being low-cost. Conformal next generation phased array radar based on flexible electronics is an example for defense applications. High quality passive components can be easily fabricated on a flexible substrate; however, active devices are not easy to integrate.
Thin film transistor technology (TFT) based on amorphous silicon and low-temperature polysilicon semiconductor materials deposited on a flexible substrate have shown great promises for the technology at low frequency applications. Transparent oxide film such as ZnO has also been studied to fabricate TFT but still showing low cut of frequency (fT) [see for example Y. Sun, J. A. Rogers, “Inorganic Semiconductors for Flexible Electronics”, Advanced Materials, vol. 19, pp. 1897-1916, 2007].
The foregoing active materials used in the flexible electronics suffer mainly from low carrier mobility due to non-single crystal epitaxial layer. Hence, they are not suitable for microwave and millimeter-wave applications. An Alternative approach such as assembling and transferring of single-crystalline nanostructures for example silicon nanowires on a flexible substrate have been investigated for RF and higher frequency ranges since they show transport properties better than a-Si or polysilicon. The drawback of these types of active devices is their low level of output current handling in addition to low cut off frequency for high performance applications.
TFT type GaAs MESFET was proposed in order to achieve higher cut off frequency reported fT of 1.55 GHz for 2 μm gate length [see for example J. Ahn, H. S. Kim, K. J. Lee, Z. Zhu, E. Menard, R. G. Nuzzo, and A. Rogers, “High-Speed Mechanically Flexible Single-Crystal Silicon Thin-Film Transistors on Plastic Substrates”, IEEE Electron Device Letters, vol. 27, no. 6, pp. 460-462, 20061.
Recent work based-on transformable single-crystal silicon nanomembrane on SOI substrate to a flexible substrate has shown fT of 1.9 GHz for a 4 μm gate length [see for example I-I.e. Yuan and Z. Ma, “Microwave thin-film transistors using Si nanomembranes on flexible polymer substrate”, Applied Physics Letters, vol. 89, pp. 212105, 2006; or H. C. Yuan, G. K. Celler, and Z. Ma, “7.8-GHz flexible thin-film transistors on a low-temperature plastic substrate”, Journal of Applied Physics, vol. 102, p. 034501, 2007; or Z. Ma, and L. Sun, “Will Future RFIC Be Flexible?,” IEEE Wireless and Microwave Tech. Conf. pp. 1-5, April 2009; or Lei Sun, Guoxuan Qin, Jung-Hun Seo, George K. Celler, Weidong Zhou, and Zhenqiang Ma, “12-GHz Thin-Film Transistors on Transferrable Silicon Nanomembranes for High-Performance Flexible Electronics”, Small-journal, vol. 6, no. 22, pp. 2553-2557, 2010].
However, there still exists a need for cheap, easy to manufacture flexible chips; in particular flexible chip that perform satisfactorily at high frequency.